Sen. John Ensign just wanted to keep the whole affair quiet. He gave thousands of dollars to his mistress to book hotels for their clandestine encounters. He bought cheap cellphones to communicate with her. He considered buying her Las Vegas home and tried to help her aggrieved husband’s lobbying career to make the whole matter go away.

But his efforts to sweep the affair under the rug eventually backfired, unraveling a once-promising Senate career that ended with an embarrassing resignation last month and new allegations that he broke a series of federal laws with his coverup.

It all spilled out on the Senate floor Thursday when the Select Committee on Ethics released in stark detail a series of damaging allegations, in the most extensive ethics investigation of a senator in nearly two decades.

The 68-page report was not only explosive in its conclusions — it alleges Ensign violated Federal Election Commission rules and campaign finance law and obstructed the Ethics Committee investigation. It was salacious in detail, alleging an almost obsessive pursuit by Ensign of Cindy Hampton, a former aide, and his attempts to pay off Hampton’s family as part of what the ethics panel called a “web of deceit.”

The committee referred the findings to the Justice Department and the FEC to investigate the possible violations.

“These findings are so disturbing … that had Sen. Ensign not resigned and had we been able to proceed to that adjudication, that it would have been substantial enough to warrant the consideration of expulsion,” Ethics Committee Chairwoman Barbara Boxer (D-Calif.) said on the Senate floor.

Since 1789, only 15 senators have been expelled from the body — and 14 of those were charged with supporting the Confederacy during the Civil War. Other senators like Ensign have resigned to avoid potentially harsh sanctions by the committee.

In a report prepared by special counsel Carol Elder Bruce, the committee laid out eight findings, saying that there is “substantial credible evidence” that Ensign violated federal law, Senate rules and his own office polices in the fallout of the affair, which ended in August 2008.

In particular, the committee said Ensign “conspired to violate and aided and abetted” Hampton to violate a moratorium on lobbying for former aides. It said there is ample evidence a $96,000 payment by Ensign’s parents to the Hamptons was severance, which federal law requires to be disclosed publicly. There were, additionally, tens of thousands of dollars in previously undisclosed payments to the Hamptons before the affair began, according to the report.

The ethics report paints a vivid portrait of how an affair between a senator and his aide unraveled into a full-blown scandal involving pursuits in an airport parking lot, cash payoffs and numerous interventions by friends and colleagues.

In one passage of the report, Ensign’s “spiritual adviser,” Tim Coe, called Ensign from outside of a hotel room where the senator was with Cindy Hampton and told him: “I know exactly where you are. I know exactly what you are doing. Put your pants on and go home.

The report said Ensign engaged in obstruction of justice by destroying documents and emails relevant to the investigation — and that he engaged in sexual harassment against the Hamptons and discriminated on the basis of gender against Hampton.

“Sen. Ensign had enormous power over Ms. Hampton,” the report said. “He controlled the sole sources of income for both Ms. Hampton and her husband. He controlled separate payments made on the Hamptons’ behalf so that their children could attend an expensive private school with the Ensign children.”

Ensign, a 53-year-old Christian conservative with a wife and three children, admitted to the affair in June 2009, forcing him to relinquish his GOP leadership spot and abandon any hope of running for president. Shunned by his colleagues and facing pressure from the committee, Ensign abruptly cut his second Senate term short, resigning his seat last week and giving way to a new senator, former GOP Rep. Dean Heller.

The report details how the Hamptons and Ensign had an intertwined personal and professional life — the senator and his mistress’ husband, Doug Hampton, were “addicted to golf” — and regularly vacationed together, including to the Ensigns’ lake house in Barstow, Calif. Cindy Hampton testified that it was the “dream” of her family and the Ensigns to “always live by each other.”

The extramarital affair began after the Hamptons’ Nevada home was burglarized in November 2007 and Ensign allowed their family to stay at his home.

The report said Ensign initiated the affair by contacting Cindy Hampton, saying he was “very persistent and relentless” and that Hampton testified that the senator wouldn’t stop, he “kept calling and calling” and he “would never take no for an answer.” Hampton testified that she was worried about losing her job as the senator’s campaign treasurer once the affair began.

In a “public confession” in Ensign’s journal, he wrote that the affair lasted from December 2007 until August 2008 and that his wife, Darlene, and Doug Hampton “had caught us several times and finally agreed that Doug and Cindy would have to leave my employ,” according to the report.

When Hampton learned of the affair by reading a text message from the senator on his wife’s phone in December 2007, he jumped out of his car and chased the senator in an airport parking lot, the report said. Cindy Hampton sat in the airport for hours and later took a taxi home.

Still, Ensign quietly carried on the affair, giving her $3,000 in cash to buy Las Vegas hotel rooms for their liaisons. He put fake events on his calendar so he could secretly meet with her.

On multiple occasions, he told her that he wanted to marry her — including when they attended the National Prayer Breakfast in Washington. During an official Senate trip to Iraq in February 2008, he repeatedly called Hampton, totaling nearly $1,000 in telephone bills.

When both Hamptons confronted the senator in his home to talk about the affair, Ensign professed his love for Cindy — and that “Doug could not work for him any longer,” the report said.

After telling his wife about his lingering feelings for Cindy Hampton, Ensign temporarily moved in with his parents — but the affair continued, including after he purchased two new cellphones so the two could communicate exclusively with one another. He typed in her name as “Aunt Judy” on his cellphone.

When his wife, Darlene, became aware of the 76 text messages he exchanged with Hampton, Ensign disconnected the phones. He wanted to buy two more, but Hampton declined. He later created fake email accounts and secretly called her from the Senate gym, the Capitol and on fundraising trips to New York.

After Doug Hampton left his employ, Ensign helped him set up a lobbying career — and Hampton immediately began lobbying Ensign, in apparent violation of a federal ban affecting former aides. Ensign took official action to help Hampton’s career, the report said, including in a 2008 meeting with Switch Communications, urging the Nevada company to sign on with Hampton because of his “valuable” federal experience.

The report said that Ensign used the power of his office to “intimidate and cajole” his constituents into hiring Hampton as a lobbyist. When a Las Vegas developer refused to hire Hampton, based on the advice of a prominent GOP consultant, Sig Rogich, Ensign wanted his chief of staff to “jack [Rogich] up to high heaven and tell him he is cut off from the office and never to contact” the senator again.

Granted immunity to testify before the committee, John Lopez, Ensign’s former chief of staff, said that he recalled “feeling like that was abusing the office.”

On at least 12 separate client issues, Hampton allegedly contacted Ensign’s office in violation of the one-year lobbying ban — and there were at least 30 improper contacts altogether in that timespan, the report said.

Hampton lobbied Ensign’s staff directly on behalf of clients like Allegiant Air — and Ensign allegedly pushed Transportation Department officials to help on issues critical to the company.

Hampton himself was indicted in March for lobbying Ensign and his staff on behalf of the Las Vegas airlines and an energy firm — in an alleged violation of a federally required cooling off period for former aides.

The only other sitting senator whose role was detailed in the report is Oklahoma Republican Tom Coburn, who lived with Ensign at the time of the affair and acted as an intermediary between the Nevada Republican and Doug Hampton.

The report disclosed that Coburn spoke to Hampton’s attorney, Daniel Albregts, on three separate occasions on May 22, 2009, to discuss a potential financial deal with Hampton. Sitting on his tractor at his home mowing his lawn, Coburn received a phone call from Albregts, who proposed an $8 million settlement for the Hamptons.

Coburn called the offer “absolutely ridiculous” and later suggested that Ensign buy the Hamptons’ Las Vegas home. Hampton later proposed that Ensign purchase the home for $1.2 million and provide another $1.6 million to the couple to restart their careers.

Ensign declined the offer, prompting an angry Hampton to alert Fox News to the sordid affair. When former Sen. Rick Santorum (R-Pa.), then a contributor to the station, learned of Hampton’s efforts, he tipped off Ensign. The Nevada Republican assembled his staff for a late-night meeting in June 2009, and announced the affair at a Las Vegas news conference the following day.

Cindy Hampton, who has recently filed for bankruptcy, is now moving to California and looking to work for a Christian group, the report said.